Quantum dots, derived from two-dimensional (2D) materials, have shown promising applications in bioimaging, photocatalysis, biosensors and white light emission devices (W-LEDs). Herein, this work involves producing a high photoluminescence quantum yield (PLQY) for 2D transition metal carbide MXene (nitrogen-doped, N-doped Ti₃C₂) quantum dots using Ti₃C₂ as a precursor and ethylenediamine as a nitrogen source. The hydrothermally treated N-doped Ti₃C₂ quantum dots developed in this study have an average size of 3.4 nm and a PLQY of up to 18.7%, which is by far the highest QY reported to date. The mechanism of the enhanced PLQY of the N-doped Ti₃C₂ quantum dots is systematically discussed by using comprehensive spectroscopic techniques (e.g. grazing incidence X-ray diffraction (GIXRD)) and complementary density functional theory (DFT) calculations. Furthermore, the N-doped Ti₃C₂ quantum dots are applied as an ultra-sensitive heavy iron ion (Fe³⁺) detector probe with a detection limit of up to 100 μM. Additionally, the as-developed MXene quantum dots have huge prospects in biological sensing by functioning as an appealing mediator-free biosensor for the detection of H₂O₂ with high sensitivity. Overall, this work will provide a blueprint for the design of 2D-QDs based on MXene toward meeting the continuous upsurge in demand for a plethora of technological applications such as electronics, solar cells, optical, biomedical, and environmental fields.

An electrically conductive and electrochemically active composite paper of graphene nanosheet (GNS) coated cellulose fibres was fabricated via a simple paper-making process of dispersing chemically synthesized GNS into a cellulose pulp, followed by infiltration. The GNS nanosheet was deposited onto the cellulose fibers, forming a coating, during infiltration. It forms a continuous network through a bridge of interconnected cellulose fibres at small GNS loadings (3.2 wt%). The GNS/cellulose paper is as flexible and mechanically tough as the pure cellulose paper. The electrical measurements show the composite paper has a sheet resistance of 1063 Ω □⁻¹ and a conductivity of 11.6 S m⁻¹. The application of the composite paper as a flexible double layer supercapacitor in an organic electrolyte (LiPF₆) displays a high capacity of 252 F g⁻¹ at a current density of 1 A g⁻¹ with respect to GNS. Moreover, the paper can be used as the anode in a lithium battery, showing distinct charge and discharge performances. The simple process for synthesising the GNS functionalized cellulose papers is attractive for the development of high performance papers for electrical, electrochemical and multifunctional applications.

Oxygen evolution reaction (OER) is a pivotal step for many sustainable energy technologies, and exploring inexpensive and highly efficient electrocatalysts is one of the most crucial but challenging issues to overcome the sluggish kinetics and high overpotentials during OER. Among the numerous electrocatalysts, metal-organic frameworks (MOFs) have emerged as promising due to their high specific surface area, tunable porosity, and diversity of metal centers and functional groups. It is believed that combining MOFs with conductive nanostructures could significantly improve their catalytic activities. In this study, an MXene supported CoNi-ZIF-67 hybrid (CoNi-ZIF-67@Ti₃C₂T_x) was synthesized through the in-situ growth of bimetallic CoNi-ZIF-67 rhombic dodecahedrons on the Ti₃C₂T_x matrix via a coprecipitation reaction. It is revealed that the inclusion of the MXene matrix not only produces smaller CoNi-ZIF-67 particles, but also increases the average oxidation of Co/Ni elements, endowing the CoNi-ZIF-67@Ti₃C₂T_x as an excellent OER electrocatalyst. The effective synergy of the electrochemically active CoNi-ZIF-67 phase and highly conductive MXene support prompts the hybrid to process a superior OER catalytic activity with a low onset potential (275 mV vs. a reversible hydrogen electrode, RHE) and Tafel slope (65.1 mV∙dec⁻¹), much better than the IrO₂ catalysts and the pure CoNi-ZIF-67. This work may pave a new way for developing efficient non-precious metal catalyst materials.